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1 Hour Exam 2 Page 1 1. Consider the van der Waals gas equation where a and b are the van der Waals constants: an P V 2 2 (V nb) nrt Which of the following statements concerning the van der Waals equation and real gases is false? a) A term is added to the measured pressure (P) in the van der Waals equation in order to correct for the effect of intermolecular forces in real gases. b) A term is subtracted from the measured volume (V) in the van der Waals equation in order to correct for the effect that real gas molecules have a finite volume. c) One would expect CH 4 to have a larger a constant value in the van der Waals equation as compared to H 2 O. d) One would expect Xe to have a larger b constant value in the van der Waals equation as compared to Ne. e) At high temperatures, the effect of intermolecular attractions in real gases are minimized and the gas behaves more ideally. 2. The effusion rate of an unknown gas is determined to be 4 ml/min. Under the same conditions, the effusion rate of CH 4 is 8 ml/min. Which of the following could be the unknown gas? a) H 2 (molar mass = 2 g/mol) b) He (molar mass = 4 g/mol) c) O 2 (molar mass = 32 g/mol) d) SO 2 (molar mass = 64 g/mol) 3. The alkenes are compounds composed of carbon and hydrogen having the general formula C n H 2n, where n is some whole number greater than one. If gram of any alkene is combusted in excess oxygen, what number of moles of H 2 O is formed? a) mol b) mol c) mol d) mol e) mol 4. How many of the following five compounds is/are not strong electrolytes? PCl 5 H 2 CO 3 HNO 3 H 2 O C 12 H 22 O 11 a) zero (All are strong electrolytes.) b) one c) two d) three e) four (4 of the compounds are not strong electrolytes.)

2 Hour Exam 2 Page 2 5. If the molecules in 1.0 L sample of hydrogen gas and 1.0 L sample of oxygen gas and 1.0 L sample of carbon dioxide gas are all moving with the same average velocity, which gas sample is at the highest temperature? a) H 2 b) O 2 c) CO 2 d) The temperature is the same in all three of the gas samples. 6. Tryptophan is one of the 20 standard amino acids and contains 64.69% C, 5.92% H, 13.72% N, and 15.67% O by mass. What is the empirical formula of tryptophan? a) C 12 H 24 N 2 O 2 b) C 11 H 12 N 2 O 2 c) C 6 H 10 NO d) C 11 H 12 NO e) C 12 H 16 N 2 O 2 7. In each of the following pairs, which compound will have the higher boiling point? CO 2 vs. COS CH 4 vs. SiH 4 KCl vs. HI a) CO 2 ; SiH 4 ; KCl b) COS; CH 4 ; HI c) CO 2 ; CH 4 ; KCl d) COS; SiH 4 ; KCl e) CO 2 ; SiH 4 ; HI 8. Equal masses of three different gases, X, Y, and Z, are mixed in a sealed rigid container at constant temperature. If the molar mass of gas X is greater than either of the molar masses of gases Y or Z, which of the following statements about the partial pressure of gas X is true? Assume ideal gas behavior. a) The partial pressure of gas X is equal to 1/3 of the total pressure. b) The partial pressure of gas X is less than 1/3 of the total pressure. c) The partial pressure of gas X is greater than 1/3 of the total pressure. d) The partial pressure of gas X may be equal to or less than or greater than 1/3 of the total pressure. 9. In a 3.00 liter rigid container at 25C, 1.23 moles of O 2 gas and 3.20 moles of solid C (graphite) are reacted to form CO gas. After the reaction has gone to completion, what will be the final pressure in the container at 25C? a) 5.01 atm b) 26.1 atm c) 10.0 atm d) 1.68 atm e) 20.1 atm

4 Hour Exam 2 Page How many of the following five compounds exhibit only London dispersion forces and no other type of intermolecular forces? NaF, CaF 2, CrF 3, CF 4, HF a) 1 b) 2 c) 3 d) 4 e) 5; all only exhibit London dispersion forces. 17. A 27.0 g sample of an unknown hydrocarbon was burned in excess oxygen to form 88.0 g of CO 2 and 27.0 g of H 2 O. Which of the following is a possible molecular formula? a) CH 4 b) C 2 H 2 c) C 4 H 3 d) C 4 H 6 e) C 4 H How many moles of O 2 (g) in the presence of excess P (phosphorus) are needed to produce 14.2 g of P 4 O 10 (molar mass = g/mol)? a) mol b) mol c) mol d) mol e) mol 19. Which of the following statements is true? a) Because more intermolecular forces are broken when water vaporizes than when ice melts, ΔH vaporization (in kj/mol) should be greater than ΔH fusion (in kj/mol). b) As the size of a covalent molecule increases, the strength of the London dispersion forces decreases. c) Molecules which exhibit hydrogen bonding intermolecular forces have unusually low melting points. d) A polar covalent compound will generally have a lower vapor pressure at some temperature than an ionic compound. e) In general, the strength of the intermolecular forces exhibited in the gaseous state are much stronger than the intermolecular forces exhibited in the liquid or solid state. 20. Consider the following reaction: Zn(s) + 2 HCl(aq) ZnCl 2 (aq) + H 2 (g) If the reaction has a 68.4% yield, how many grams of zinc (MM = g/mol) are needed to obtain an actual yield of 1.00 g of zinc chloride (MM = g/mol)? a) 7.01 g b) 1.40 g c) g d) g e) g

5 Hour Exam 2 Page You are holding two balloons, one blue and one orange. The blue balloon contains He and is 4 times the volume of the orange balloon. The orange balloon contains Ne. Which of following best represents the mass ratio of He:Ne in the balloons? Assume constant temperature and pressure. a) 4:5 b) 5:4 c) 4:1 d) 1:4 e) 20:1 22. Consider 2 reactants, A and B. The molar mass of A is greater than the molar mass of B. You add equal masses of A and B together and let them react. Which of the following statements (a-d) must be true? a) Reactant A must be limiting. b) Reactant B must be limiting. c) If the coefficient for B is greater than the coefficient of A in the balanced equation, then reactant B must be limiting. d) If the coefficient for A is greater than the coefficient of B in the balanced equation, then reactant A must be limiting. e) None of the above choices must be true. 23. A 9.00 L flask containing neon gas at 2.00 atm and a 3.00 L flask containing helium gas at 4.00 atm are connected by valve (see figure below): Ne He 9.00 L 3.00 L 2.00 atm 4.00 atm After the valve between the two flasks is opened and the two gases have time to mix, which of the following statements regarding the partial pressures of Ne and He is true? Assume constant temperature and assume that no chemical reaction occurs between Ne and He. a) The partial pressure of neon is 1.50 times greater than the partial pressure of helium. b) The partial pressure of neon is 2.00 times greater than the partial pressure of helium. c) The partial pressure of helium is 1.50 times greater than the partial pressure of neon. d) The partial pressure of helium is 2.00 times greater than the partial pressure of neon. e) The partial pressures of helium and neon are equal.

7 Hour Exam 2 Page Consider the following two gas samples: Sample A contents = Cl 2 (g) n = 1 mol T = 300 K P = 0.4 atm Sample B contents = O 2 (g) n = 1 mol T = 3000 K P = 0.2 atm Which of the following statements is true regarding these two gas samples? a) The gas in sample B should behave more ideally than the gas in sample A. b) The volume of the gas in sample B is five times larger than the volume of the gas in sample A. c) The average kinetic of the gas molecules in Sample A is larger than the average kinetic energy of the gas molecules in Sample B. d) The average velocity of the gas molecules in Sample A is greater than the average velocity of the gas molecules in Sample B. e) The number of gas molecules in Sample A is larger than the number of gas molecules in Sample B. 29. A 5.00 g sample of an unknown metal chloride compound is dissolved in 50.0 ml of solution. To this solution, 70.0 ml of M Pb(NO 3 ) 2 is added in order to precipitate all of the chloride ion as PbCl 2 (s). Calculate the mass percent of chloride ion in the metal chloride compound. a) % b) 14.0% c) 19.9% d) 28.0% e) 39.7% 30. A 5.00 g sample of iron reacts with oxygen in the air to form 6.91 g of an oxide of iron. What is the empirical formula for this compound? a) FeO b) Fe 2 O c) Fe 2 O 3 d) Fe 9 O 13 e) Fe 3 O My answers for this Chemistry 102 exam should be graded with the answer sheet associated with: a) Form A b) Form B c) Form C d) Form D e) Form E

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